Patent Application
20090211620
Solar cells are appearing in more and more products as the cost per watt decreases through high volume manufacturing processes and increasing conversion efficiency increase. Much of the research in the solar industry has focused on increasing efficiency of the modules, ordered arrays of solar cells units, in conversion of sunlight into electrical energy. Solar cells units, or solar modules on a smaller scale than conventional grid-tied modules and panels, have been applied to existing products in an ad-hoc manner wherever a benefit could be achieved from relatively lower power generation. Some of these products benefiting from solar cells include stationary applications such as landscape lighting, and construction signage. More mobile applications include flexible solar cells woven into clothing for charging portable electronics and flexible solar modules that can be unfolded to provide power in remote locations off-grid, such as recreational vehicles and camping lanterns.
In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.
A mesh including strips of solar cell unit material may be conformed to fit a curved surface. The strips of solar material may be cut from a specifically designed modular type array of solar cells formed on a flexible backing, such as Mylar or thin metal foil such as aluminum. The strips of solar material may then be weaved or tied with other flexible strips to form a mesh. The mesh may take the form of a fabric or net. The mesh may be applied to a curved surface in a conformal manner, thus allowing a product to be designed independently of the exact location of the light source, with the mesh then being applied to the finished design of the product. In some embodiments, the mesh may have solar strips and other non-solar strips woven in a manner to form a pleasing design as opposed to optimized for solar conversion efficiency. Color may be introduced into the mesh independent of the solar strip manufacturing chemistry to add further aesthetic design capability.
Products incorporating solar materials have not generally been designed from an aesthetic point of view. Some embodiments of the present invention allow such design at least because of the ability to design aesthetically pleasing meshes from both color and texture perspectives, and the ability to conform them to a large variety of surfaces.
In one embodiment, either material may be a warp or weft according to classic weaving terms. In one embodiment, second strips 120 may be formed of a stronger or more durable material, and may be used as a warp in a manufacturing process, with the first strips of solar cell material woven into them to form a fabric or net. In one embodiment, the second set of strips 120 may be at least partially transparent to maximize light collection by the set of solar cell strips. Pigments may be included in the strips, or in an epoxy like encapsulation of the mesh when applied to a desired surface to further increase aesthetic design flexibility and protect the solar material from ultraviolet radiation.
The warp pitch and weft pitch is given by the width of the warp and weft strips plus the spacing between the strips, respectively. That is,
Pitch of Warp=Warp strip width+Warp spacing
Pitch of Weft=Weft strip width+Weft spacing
An example of a closed mesh, which defines a fabric article, is the case where either the warp or weft spacing is about 0 mm. Cases when both pitches are greater than 0 mm results in a net weave. The mechanical properties of the mesh, namely the flexibility and conformability, and the electrical output of the solar cell strips, namely the total power generation, are inter-related through the physical and electrical attributes of the warp and weft. For example, the pitch of the warp and weft directly influence mechanical properties, namely flexibility, while the detailed nature of solar cell units in the strip design directly influence the collective voltage and currents of the mesh, namely power generation, just as in solar cell module design.
It is assumed that the intensity of light available on the surfaces of solar cell strips within the mesh will, in general, be non-uniform, as the mesh as whole may be used outdoor on curved surfaces. Non-uniform illumination in an array of solar cell units causes ‘shading effects’, which can lead to array failure when operating at high current levels. The flexible mesh described here may have an array operating at lower current levels such that the mesh or array does not suffer from the same shading heating effects as in conventional solar cell modules.
Similarly, individual solar cell units in a flexible strip may be in series and typically possess low shunt resistance and high reverse current character. These electrical properties imply that if a particular solar cell unit in a strip is completely shaded by a strip above it, the photo-generated current from other illuminated units may still pass through the shaded unit. Hence, solar cell strips with periodic dark or shaded area, as determined by the pitch in the opposite weave, will not have the effect of eliminating photo-generated current in a strip.
In one embodiment, the first strips of solar material 110 may be cut from a solar panel. The solar panel may be formed using thin film processes to produce solar cells on a flexible substrate, such as Mylar or metal foil. The resulting commercially available panels are somewhat flexible, as the solar cells may have a thickness of about 1 μm. The additional substrate may also be flexible. The strips may be cut using a knife, laser, or any other method desirable.
Optimization of mechanical and electrical performance of a mesh of strips collectively may be obtained by selecting the dimensions and solar cell diode layout within the solar cell panel consistent with the strips to be obtained from the panel. The strips may be cut and woven to form a mesh optimized for a specific product. When the strips are woven together to form a net or fabric, the resulting net or fabric may be more flexible than the original solar panel. Thinner strips may be used to further increase the flexibility of the resulting mesh. Different weaves may also be utilized to allow for a more flexible and hence conformable mesh, such as a fabric or net.
In one embodiment, the strips may be tied or otherwise coupled at selected locations to form a mesh 200 in the form of a net as illustrated in
As a very basic example embodiment, the mesh 200 in
As a specific example of a fabric design in
In a further embodiment, each strip is capable of generating 0.011 amps under normal operating conditions, and there are 8 strips in all, resulting in a potential operating output current could of 0.088 amps at 3.0 volts. Thus, the potential power is 0.26 watts without consideration of shadowing effects from the interleaved strips. In still further embodiments, mesh 200 may be considered an example of a basic mesh module, where modules may be combined for additional power output.
The operational power output of a mesh, with interleaved shading effects, is estimated by considering the area shaded. For one example embodiment, where there are an equal number of strips in each the warp and weft and all strips have approximately the same width, the total shaded in the design is given by 8×0.5″×0.5″=2 in2. The total active area of the solar cell strips is given by is given by 4″×2″=8 in2. Assuming the maximum available power is roughly given by the illuminated area, and the illuminated area is reduced by 25% from interleaved shading effects, then the operational power level is estimated to be 75% of the normal operational power level. The power output for this design with the shading effect is then about 0.19 watts.
Typical lengths for the strips of solar materials range from 15 cm to 90 cm. Lengths of at least up to 45 m or longer may be used in further embodiments. In some embodiments, a strip may contain several cells that are coupled in series to provide a desired voltage. The width of a strip is proportional to the amount of current that can be provided. The width of the strip may be a trade off between several factors, including aesthetic factors, conformal factors, and current factors. Typical widths of the solar strips range from less than 0.5 cm to about 3 cm. Wider widths may be used if desired, such as for use in covering very large surfaces, which may be viewed from a distance. Aesthetic design desires may lead to the use of a larger width for viewing at a distance. The use of strips of solar material in a mesh provides great flexibility to accomplish aesthetic design desires.
A further embodiment involves the electrical properties of the solar cells themselves. Normally, a by-pass diode is required in modules to accommodate shading effects and prevent overheating and possible destruction. Such a by-pass diode routed current around the shaded solar cell. Additionally, to maximize the efficiency in solar cells, the cells are typically designed to have a high shunt resistance. In thin film flexible solar cells used in applications where shading may occur during a significant portion of the operational lifetime, a lower shunt resistance is advantageous. A solar cell with relatively low shunt resistance will allow current to pass through it even when 100% shaded, as it then operates as a series resistor, rather than preventing photo-generated current from flowing altogether, which could be the case for an ideal solar cell diode.
The graph in
The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
